An oil sand is usually a mixture of clay, silicates, water and hydrocarbons. The oil phase contained at up to about 18% in oil sands, consisting of various hydrocarbons, has a widely varying composition often specific to the mining region; it may contain bitumen, crude oil and asphalt. Processing of oil sand is carried out with the aim of separating the rock or sand fraction comprising clay and silicates from the actual useful material, i.e. the oil phase comprising the hydrocarbons.
Oil sands are often extracted by surface mining. For mining from deeper strata, preliminary processing is often carried out with steam being fed into the deposit, the hydrocarbons being liquefied, collected at well sites and brought to the surface.
U.S. Pat. No. 4,240,897 describes a method for extracting bitumen from oil sand by means of hot water.
DE 10 2007 039 453 A1 describes a method for obtaining bitumen from oil sand/water mixtures by means of flotation.
According to the so-called CLARK-ROWE process, oil sand is mixed with caustic soda and the oil phase is thereby mobilized. Water-oil phase separation takes place primarily by flotation. The remaining rock or sand component still contains up to 10% of the oil phase after extraction, some of which is adsorptively bound to the surface of the very fine particles. This leads to steric stabilization of these particles in the effluent flow of the process, so that separation of these particles is made very difficult. Furthermore, a significant amount of clay is hydrophobized by adsorptive accumulation of the oil phase to such an extent that during flotation it enters into the product, i.e. the separated oil phase. There, the clay constitutes a quality-reducing contaminant which can only be separated again with difficulty. Depending on the oil sand composition, about three to four times the amount of nonrecyclable fresh water is therefore required in order to obtain one barrel of oil phase. The water is temporarily or permanently stored with the separated rock or sand fraction in collection tanks.
U.S. Pat. No. 4,968,412 describes a two-stage method for removing bitumen from oil sand, in which addition of organic solvents and separation of the clay take place in a first step. In a second step, washing of the processed oil sand is carried out with water while adding surfactant.
US 2008/0060978 A1 describes a method for extracting hydrocarbons from oil sand, in which the oil sand is mixed with organic solvents and delivered to a centrifugal separator.
U.S. Pat. No. 3,542,666 describes a method for extracting hydrocarbons from oil sand, in which organic solvents in combination with a small quantity of water in particular quantity ratios are mixed with the oil sand to form a suspension, and the pH of the suspension is adjusted to at least 5 before filtration of the suspension is carried out.
U.S. Pat. No. 4,071,433 likewise describes a method for extracting hydrocarbons from oil sand, in which the oil sand is suspended in a tank with the aid of oil. The suspension is subsequently divided into one subflow containing coarse sand and a further subflow containing fine sand, which are treated differently.
WO 2009/038728 A1 discloses a method for extracting organic substances containing hydrocarbons from oil sand. Here, the oil sand is wetted with a liquid containing turpentine and the liquid with extracted hydrocarbons is separated from residual material.
U.S. Pat. No. 4,539,097 describes a method for separating mined oil sand from a solution comprising organic solvents and bitumen by means of hydrocyclones.
US 2008/0210602 A1 describes a method for separating bitumen from oil sand by using various organic solvents, which are added to the oil sand in different solution stages or settling tanks. This is followed by vacuum filtration and recovery of the solvents used.
U.S. Pat. No. 3,338,814 describes another method for separating oil from oil sand, a froth which is produced, containing bitumen, being dewatered and the resulting dehydrated material flow subsequently being hydrocycloned.
U.S. Pat. No. 4,603,115 describes an automated analysis method for sequential solvent extraction, an ultrasound treatment of the substance to be analyzed and the respective solvent being carried out.
One problem with the extraction of hydrocarbons from oil sands with the aid of organic solvents resides inter alia in the processing the separated rock or sand fraction still containing solvent.